docs: def url_join(url, path):
      """ url version of os.path.join
      """
      p = six.moves.urllib.parse.urlparse(url)
  
      t = None
      if p.path and p.path[-1] == '/':
          if path and path[0] == '/':
              path = path[1:]
          t = ''.join([p.path, path])
      else:
          t = ('' if path and path[0] == '/' else '/').join([p.path, path])
  
      return six.moves.urllib.parse.urlunparse(
          p[:2]+
          (t,)+ # os.sep is different on windows, don't use it here.
          p[3:]
      )